This invention relates to a method of and apparatus for measuring distance in numerically controlled machine tools.
It is known in numerically controlled machine tools to carry out both machining operations and measuring operations on a workpiece held in the machine. For the purpose of the measuring operation, the known machine includes a probe having a stylus whereby to sense a selected surface of the workpiece. The probe outputs a signal response to such sensing. The signal is communicated to a numerical position control system of the machine thereby enabling that system to determine the position of the probed surface and thus the dimension of that surface in relation to a predetermined datum. When the probe is to be taken into use it is necessary to remove the last used tool from the operative position and introduce the probe in the position previously occupied by the tool. For example, if the tool and the probe are mounted at respective stations of a multi-station turret, the latter has to be indexed to bring the probe into the operative position. If the machine has an automatic tool change mechanism which moves the tools between the tool holder of the machine and a magazine of such tools, the tool has to be returned to the magazine and the probe has to be moved from the magazine to the tool holder before the measuring operation can be carried out. The need to exchange the tool for the probe and vice versa can be a source of delay, and is otherwise disadvantageous, especially in the case where the measuring operation has to be carried out between successive machining operations. Further, different surfaces of the same workpiece often have different shapes or orientations, requiring differently-shaped tools and correspondingly different styli for sensing of those surfaces. This, in turn, may require different probes to be held in said turret or said magazine.